1. Technical Field
The present disclosure relates to a frequency modulator, and more specifically to a clock frequency modulator.
2. Description of the Related Art
Devices adapted to modulate a clock frequency are known. A typical application for frequency modulators are switching regulators. A serious problem for switching regulators are the electromagnetic interferences (EMI) generated especially because of their fast switching features.
One approach to reducing electromagnetic interferences consists in the periodic or random modulation of a parameter of the signals which are applied to switching devices, such as the switching frequency. The parameter oscillates with small amplitudes around a nominal value so that the power of the harmonics is distributed on the spectrum. In order to reduce the emissions of electromagnetic interferences of the regulator and reduce the cost and size of the line filters, the switching frequency thereof needs to be modulated so that the resulting action on the distribution spectrum allows the distribution of the energy of each harmonic of the switching frequency on a number of sideband harmonics that have the same energy though a smaller amplitude.
A typical frequency modulator circuit adapted to generate a low-frequency triangular waveform is shown in FIG. 1. The circuit includes a capacitor C which is connected to ground GND and to a current generator Ic connected to a supply voltage Vdd and to a switch S that may be connected to another current generator Icc that is connected to ground GND. The capacitor is also connected to the non-inverting terminal of a hysteresis comparator Comp having the inverting terminal connected to a reference voltage Vref. The output voltage of the comparator Comp controls the closing or opening of the switch S for the generation of a triangular wave on the non-inverting terminal of the comparator Comp. In order to modulate the frequency, the circuit topologies generally use the triangular waveform generated in this way as a modulating reference voltage to control the oscillation frequency of the main oscillator.
In a completely integrated clock frequency modulator a low-frequency triangular wave needs to be generated without using external components. The triangular waveform is the modulating reference voltage that may be used to vary a circuit parameter of the oscillator so that the frequency of the oscillator is modulated by the modulating signal.
In view of the state of the art, a clock frequency modulator that is simpler than the known frequency modulators and that may be integrated needs to be provided.